Dnp Applications - Siemens RUGGEDCOM ROX II User Manual

RUGGEDCOM ROX II
CLI User Guide
Port Numbers
The TCP port number dedicated to Modbus use is port 502. The Modbus TCP Server application can also be
configured to accept a connection on a configurable port number. This auxiliary port can be used by masters that
do not support port 502.
Retransmissions
The Server Gateway offers the ability to resend a request to a remote host should the remote host receive the
request in error or the Server Gateway receives the remote host response in error.
The decision to use retransmissions, and the number to use, depends upon factors such as:
• The probability of a line failure.
• The number of remote hosts and the amount of traffic on the port.
• The cost of retransmitting the request from the server versus timing-out and retransmitting at the master. This
cost is affected by the speed of the ports and of the network.
ModBus Exception Handling
If the Server Gateway receives a request for an un-configured remote host, it will respond to the originator with a
special message called an exception (type 10). A type 11 exception is returned by the server if the remote host
fails to respond to requests.
Native Modbus TCP polling packages will want to receive these messages. Immediate indication of a failure can
accelerate recovery sequences and reduce the need for long timeouts.
Section 3.20.1.3

DNP Applications

RUGGEDCOM ROX II supports Distributed Network Protocol (DNP) version 3.0, commonly used by utilities in
process automation systems. DNP3 protocol messages specify source and destination addresses. A destination
address specifies which device should process the data, and the source address specifies which device sent
the message. Having both destination and source addresses satisfies at least one requirement for peer-to-peer
communication since the receiver knows where to direct a response.
Each device supporting DNP must have a unique address within the collection of devices sending and receiving
DNP messages.
Address Learning for DNP
RUGGEDCOM ROX II implements both local and remote address learning for DNP. A local Device Address Table
is populated with DNP Addresses learned for local and remote DNP devices. Each DNP address is associated
with either a local serial port or a remote IP address.
When a message with an unknown DNP source address is received on a local serial port, the DNP source
address and serial port number are entered into the Device Address Table. When a message with an unknown
DNP source address is received from the IP network, on the IP interface that is configured as the DNP learning
interface, the DNP source address and the IP address of the sender are entered into the Device Address Table.
When a message with an unknown DNP destination address is received on a local serial port, the message is
sent in a UDP broadcast to the network interface configured as the DNP learning interface. When a message with
DNP Applications
Chapter 3
Device Management
113